39. Most archaeologists have held that people first reached the Americas less than 20,000 years ago by crossing a land bridge into North America. But recent discoveries of human shelters in South America dating from 32,000 years ago have led researchers to speculate that people arrived in South America first, after voyaging across the Pacific, and then spread northward. Which of the following, if it were discovered, would be pertinent evidence against the speculation above? A. A rock shelter near Pittsburgh, Pennsylvania, contains evidence of use by human beings 19,000 years ago. B. Some North American sites of human habitation predate any sites found in South America. C. The climate is warmer at the 32,000-year-old South American site than at the oldest known North American site. D. The site in South America that was occupied 32,000 years ago was continuously occupied until 6,000 years ago. B E. The last Ice Age, between 11,500 and 20,000 years ago, considerably lowered worldwide sea levels. 做完题目,再仔细一想, B中说发现北美的居民比南美的还早...的确削弱了原文的结论. 那么是不是也同时削弱了原文的提干, 比南美还早的话, 就不可能是20000年前到达的拉,应该还要早啊.... 这样把原文中的提干也一起削弱也可以么? | 
